1. Field of the Invention
This invention relates to a display apparatus for producing a color image from a digitally coded representation of the image, and to a method of coding a color image.
2. Prior Art
The display of digital pictures (from external sources, or generated by computer) is becoming a major factor among computer users and developers. Displays have evolved from simple alphanumeric terminals to more general output devices, and the concept of the APA (all-points-addressable) display is now firmly established and bit-map devices are common. Inevitably, users are asking for improved pictorial output. Simple graphic displays are no longer adequate for many applications, and many users need the capability of displaying true images.
The most common way of describing the ability of the eye (or rather, of the whole Human Visual System--HVS) to observe detail (resolution) and contrast (grey levels) is to plot a curve of contrast sensitivity against spatial frequency. This is referred to as the "frequency model" and a graph is presented later in this specification (FIG. 1). A considerable amount of work has been done on measuring this curve under various conditions, and the first part of this specification summarises the essentials of the work in this area.